While you contend that “The government labs, CIP and SAAMI all agree on this, (There is no conversion application of a correction factor between the two types of measurements which is safe.) based upon their collective experience."; I can't find and thus don't know that that agreement exists.
Let us look at your, (and Lyman's) contention.
We have pressure in the chamber of a gun.
We have two methods of measuring that pressure under discussion, copper crusher and piezoelectric. (Strain gage methods?)
If the contention is true, that there is no mathematical conversion method between the two, then one or both of the methods of measurement must be incorrect. N'est pas?
However, the contention seems to be untrue. See
http://kwk.us/pressures.html , and in particular the links.
I found Denton Bramwell's article very interesting .
Note the frequent warnings not to use and rely on any conversion formula at the upper pressure areas. This takes care of the “...which is safe.” element of the contention.
Then we have available several different conversion formulas with more than convincing r^2s that, if the user complies with the warning, provide safe and reasonably accurate conversions.
But wait, there's more.
SAAMI sets voluntary pressure standards for manufacturers, (see the link on the cite); and manufacturers are instructed to use a random sample size of 10 cartridges from a lot to measure pressure. These SAAMI pressure standards are set with at least the strength of the cartridge case and commonly used guns in mind. There seems no objective test involved in the selection of these standards.
Now a sample size of 10 and the recently-recognized problems with randomness suggest to me that any AVERAGE SAMPLE pressure measured is not a precise estimator of the POPULATION pressure. Then, for a cartridge such as the 342 Knurlman, SAAMI copper crusher pressure and piezoelectric sample pressure measurements are by absolutely not precise estimators of average pressure, meaning that the published CUP and PSI pressures are not precise. This is just part of every estimation system, not merely SAAMI, who I'm sure are doing a great job. Now, since the published pressures have variation within them, any conversion formula will be inexact because the SAAMI data is inexact.
If we set two guys up picking up rocks and estimating the weight of each rock by hand, one in pounds and the other in kilograms; then we should not be surprised to find that developing a conversion formula from pounds to kilograms shows some error. However, there is a clear and precise relationship between pounds and kilograms.
It should be noted that the conversion formula creators all make this assumption: CIP and SAAMI both set a pressure limit for a cartridge in some fashion. Then, (when they provide data for both CUP and PSI), cartridges yielding the set pressure are tested using the other method. If CUP pressure has been decided on at CC,CCC , then cartridges producing CC,CCC must be produced and then tested, yielding pressure of PP,PPP.
We assume but do not know that that has happened.
Ed Harris wrote:
The government labs, CIP and SAAMI all agree on this based upon their collective experience. If you disagree with that conclusion I recommend that you take it up with them. I am only the messenger.
I am not a qualified as a subject matter expert in this area. I only worked in the firearms industry for 14 years, and have been out of it for the last 20, so I am not fully knowledgeable of current procedures and standards. In the 1980s I worked in private and government labs firing thousands of rounds of military ammunition from 5.56-40mm and sporting ammunition in foreign technical intelligence, R&D and production QA environments. The results obtained using different test methods were never deemed comparable under any circumstances and and required different procedures and calibration standards.
That in itself could be interpreted as an apparent clue.
If you wish to make independent interpretations and develop load data based upon educated guesses I recommend extreme caution and would wish you good luck in your endeavors.